Escape From Dante's InfernoSandra D. Atchison
Few industrial technologies are as archaic as copper smelting. At Kennecott Corp.'s sprawling complex outside Salt Lake City, yellow and green flames leap from open furnaces where copper concentrate is melted. Giant caldrons of molten metal swing from cables attached to the roof. The air reeks of sulfur, which is emitted at every stage, and workers wear respirators and coveralls. "It's Dante's inferno," observes G. Frank Joklik, Kennecott's president. Indeed, the giant smelter is Utah's biggest single source of air pollution, spewing out 4,700 pounds per hour of sulfur dioxide (SO2), a prime culprit in acid rain.
By 1995, however, the fire and brimstone may be just a memory. By then, Kennecott plans to have replaced its facility with an $880 million smelter that represents the industry's biggest technology change in decades. Kennecott expects the process to cut its smelting costs--already among the industry's lowest--by 50%, and that won't be the only benefit. Using sealed furnaces and other tricks, the new technology will capture 99.9% of the sulfur in the processed ore, up from 94% now, making it the cleanest smelter in the world. Emissions of SO2 will be slashed to 200 pounds an hour, far below the 5,700 pounds allowed under Utah regulations.
The technology was developed jointly by Kennecott and a Finnish mining and engineering company, Outokumpu Oy. Instead of being processed in open furnaces, the crushed, processed ore is loaded into a closed smelting furnace, at 2,400F, where it is mixed with oxygen, causing the metal to ignite. Iron and other impurities are drawn off, while sulfur gases are funneled to a recovery plant, leaving 70% pure molten copper.
COOL PROCESS. To clean up the operation, Kennecott made a radical change from the centuries-old traditional process. Currently, the molten copper is moved from furnace to furnace in giant open ladles, spewing out clouds of sulfur gas. This is the dirtiest part of the operation, when the most SO2 escapes. Instead of transporting molten metal, the new process will rapidly cool the copper with a high-pressure water spray in an enclosed vessel, turning it into sandlike granules. "The reason nobody did it before was we didn't understand why we should deliberately cool something that was molten--only to melt it again," says David B. George, director of smelting technology, who helped to develop the process. The reason, of course, is that the solid doesn't emit any sulfur fumes.
At the next stage, Kennecott will cut emissions by replacing the traditional open converting furnaces. The black granulated metal will be fed into an enclosed converting furnace, where it will be melted, and additional impurities removed, to yield 99% pure copper. As in today's smelters, SO2 will be captured and converted to sulfuric acid, which is sold as an industrial commodity. But the SO2 drawn from the enclosed furnaces will be highly concentrated, so the recovery process will be much more efficient.
Kennecott expects startling gains. The entire process should reduce labor costs at the smelter some 40%, mainly by eliminating material-handling jobs. By capturing and recycling wasted heat energy, the plant will cut the cost of electricity--a major drain--by 75%. And while Kennecott now sends 40% of its ore concentrate to Japan for smelting, the new smelter will have twice the capacity of the old plant, enabling the company to halt those shipments.
CAREFUL STUDY. Construction of the Utah smelter, which begins in May, will cap a 10-year effort at Kennecott to cut costs, boost efficiency, and comply with increasingly tough pollution regulations. Since 1985, the nation's third-largest copper producer has made capital investments of $625 million in its facilities. Today, it costs Kennecott just 40 cents to mine and produce a pound of copper, one-third the cost a decade ago. With the new plant, smelting should cost 10 cents a pound, bringing the overall production cost down to about 35 , compared with an industry average of 60 cents to 70 cents.
As more stringent clean-air regulations take effect over the next few years, other U.S. copper producers will be under pressure to clean up their smelters. SO2 emissions from copper smelters foul not just the air around the stacks: Mixed with moisture, they can fall as acid rain hundreds of miles away. Industry experts believe most producers will try to comply with new regulations by retrofitting plants. But Kennecott is considering licensing the process, and "anyone looking at a new smelter would be looking very carefully at this," says Robert H. Lesemann, director of base metals at consultant Resource Strategies Inc. in Exton, Pa.
That may include producers abroad. Pollution regulations have been lax in copper-smelting countries in Latin America and elsewhere. But many of these are beginning to toughen their laws. So instead of shipping ore overseas for treatment, Kennecott may one day export its technology.